定语从句中,whom只能在从句中充当宾语成分,who既可当主语又可当宾语.但是若是介词后的宾语,只能用whom而不能用who.
如：there is nobody who/whom he can turn to for help.没有谁可以让他寻求帮助.这里引导词当宾语,who和whom都行,当然这里既可指人也可指物的that也可以。
但是：there is nobody to whom he can turn for help.这里引导词同样当宾语,但是位于介词to后,只能用whom,而不能用who（that同样不行）。
扩展资料
定语从句中易混淆的难点
1、在限定性定语从句中指代物时，which 和that 一般可通用。
The new house that/which I has just bought is about six miles away.
They planted some trees that /which did n't need much water.
2、限定性定语从句中只用that 而不用which 的情况。A）先行词有形容词最高级修饰时 This is the best way that has been used against pollution. Polly is the most direct young woman that I have ever come across .
B) 先行词有序数词修饰时 This is the third time that they have met. The very first time that Lester saw the film, he made up his mind to become a doctor.
